This invention relates to the conditioning of seeds, such as for example, by priming, chemical treatment and biological treatment and to the use of biologically treated seeds to recondition land and improve plant productivity.
Seed priming or osmoconditioning are terms to describe a known pre-sowing hydration treatment developed to improve seedling establishment (Heydecker and Coolbear, 1977, Seed Science and Technology 5:353-425), (Khan, et al., 1980/81, Israel J. Bot. 29:133-144) and (Bradford, 1986 HortScience 21:1105-1112).
In seed priming, the seeds are placed in an aerated osmotic media of known water potential. In this process, the osmotic solutions induce a water potential that prevents the completion of germination (radicle emergence). Seeds are, however, able to imbibe and complete the early phases of germination under limiting water content conditions. The duration of the priming treatment has been reported to b e from less than 24 hours (Guedes and Cantliffe, 1980, J. Amer. Soc. Hort. Sci. 105:777-781) to several weeks (Khan, et al., 1980/81, supra) and is dependent on species, cultivar and even seed lot. Seeds are then dried back. After priming, seeds can be sown with existing planters. Results obtained from priming different crop seeds have been reviewed by Bradford, 1986, supra. In general, seedling emergence of primed seeds is earlier an d more synchronous than dry sown seeds. Improvements in plant growth and yield characteristics have also been documented.
In the prior art priming processes, several different osmoticums have been used to achieve the water potential for priming including high molecular weight (MW of 6000-8000) polyethylene glycol (PEG) and/or inorganic salts (Heydecker and Coolbear, 1977, surra). After priming, the seeds are removed from the solution used for establishing the water potential before being dried back.
Several technical and logistical difficulties have been encountered with the prior art priming techniques. For example, osmotic solutions require continuous aeration and in general, a large volume of priming solution is required per quantity o f seeds. Reductions in percentage seedling emergen ce ha ve been reported with the use of inorganic salts (Brocklehurst and Dearman, 1984, Ann. Applied Biol. 102:585-593). A relatively high concentration of PEG in solution is viscous and has low oxygen solutibility and diffusivity (Mexal, et al., 1975, Plant Physiol. 55:20-24).
An alternative to the use of solutions is to prime seeds in a solid medium. A solid material should have a high water holding capacity and allow seeds to imbibe. Peterson (1976, Sci. Hort. 5: 207-214) described a procedure to prime onion seeds in a slurry of PEG 6000 and vermiculite. A ratio of three to four parts vermiculite moistened with PEG solution were mixed with one part seed. Although this technique overcame the need for aeration, he reported that the seeds were difficult to separate from the vermiculite. Methods have been described to increase the seed moisture content of large-seeded vegetables prior to sowing (Bennett and Waters, 1984, J. Amer. Soc. Hort. Sci. 109:623-626 and 1987, J. Amer. Soc. Hort. Sci., 112:45-49). Seed moisture content of lima beans (Phaseolus lunatus) and sweet corn (Zea Mays) was increased by combining seed, vermiculite and a known amount of water in a closed container. This mixture was incubated and then the vermiculite sieved away prior to sowing the hydrated seed. Seedling establishment was improved by the pre-sowing treatments for both crops.
Inoculation of seeds with bacteria or chemicals prior to planting is known in the art. For example, United Kingdom patent specification 849,210 discloses inoculating seeds under reduced pressure to enable penetration of the bacteria under the coat of the seed and thus survival of the bacteria for a period of time. This procedure is expensive and appears to be limited in the range of bacteria that can be inoculated into seeds.
Accordingly, it is an object of the invention to provide a novel technique for priming seeds.
It is a still further object of the invention to provide a novel technique for inoculating seeds.
It is a still further object of the invention to provide a novel technique for inoculaotng soil.
It is a still further object of the invention to provide a novel technique for inoculating soil for bioremedial purposes.
In accordance with the above and further objects of the invention, a solid phase media is used to prime seeds. The solid phase media includes a solid matrix that provides a structure to hold water and allow gas exchange. Chemical treatment and addition of microorganisms may be accomplished during priming. The seeds may be used to inoculate soil with bacteria such as for example, bacteria useful in agriculture or to breakdown contaminants in the soil and facilitate plant uptake of contaminants from soils, such as for example, radionuclides.
The solid matrix holds water with an appropriate water potential to initiate and maintain metabolism prior to germination. The temperature and aeration are at a level that reduces damage.
The seeds are then dried back and the drying back may be performed in more than one phase with aeration and moisture control interrupting the drying operation to promote healing. In one embodiment, the seeds are separated from the matrix after being dried although, in other embodiments, the seed in the matrix may be used for planting, particularly in the case of small seeds which require added matrix material for efficient use in planters or in the case where the matrix aids in the development of beneficial microbes or the beneficial application of chemicals to the seed. From the above description, it can be understood that the method, matrix and seed of this invention have several advantages such as: (1) there is a synergistic relationship with inoculation by microorganisms or the use of chemical treatment in the priming; (2) superior synchrony of emergence and speed of germination are provided; (3) a higher yield is obtained from the seeds; and (4) the priming provides a certain measure of synchronism with other techniques such as the coating of seeds for protection.